Regarding physical channels for use in an LTE (Long Term Evolution) method, as one of methods for a mobile communication system, the following five physical channels are defined as physical downlink channels for transmission from a base station to a terminal. Specifically, the five physical downlink channels are constituted by a PBCH (Physical Broadcast CHannel), a PDCCH (Physical Downlink Control CHannel), a PCFICH (Physical Control Format Indicator CHannel), a PDSCH (Physical Downlink Shared CHannel), and a PHICH (Physical Hybrid-arq (automatic repeat request) Indicator CHannel).
A PBCH is a channel for transmitting broadcast information. A PDCCH is a channel for transmitting information for decoding downlink packet data. A PCFICH is a channel for transmitting information for decoding a PDCCH. A PDSCH is a channel for transmitting downlink packet data. A PHICH is a channel for transmitting a CRC (Cyclic Redundancy Check) check result with respect to a PUSCH (Physical Uplink Shared CHannel) to be described later.
Further, in the LTE method, the following three physical channels are defined as physical uplink channels for transmission from a terminal to a base station. Specifically, the three physical uplink channels are constituted by a PRACH (Physical Random Access CHannel), a PUCCH (Physical Uplink Control CHannel), and a PUSCH.
A PRACH is a channel for transmission in order to perform electric power control while synchronizing with an uplink. A PUCCH is a channel for transmitting HARQ information to be described later, or a CQI (Channel Quality Indicator), a PMI (Precoding Matrix Indicator), or an RI (Rank Indicator) indicating a receiving quality. HARQ information is information for notifying a decoding status of a PDSCH as ACK (ACKnowledment)/NACK (Negative ACKnowledment)/DTX (Discontinuous Transmission). A PUSCH is a channel for transmitting uplink packet data, in addition to information included in a PUCCH. Note that one of a PUCCH and a PUSCH is transmitted depending on presence or absence of uplink packet data.
In the LTE method, an operation performed when a terminal receives a signal from a base station is as follows. First of all, a terminal receives a PBCH transmitted from a base station, and then receives a PCFICH. Subsequently, the terminal confirms the number of OFDM (Orthogonal Frequency Division Multiplex) symbols in which a PDCCH is mapped on the basis of a CFI (Control Format Indicator) value detected from a PCFICH, and detects whether or not a PDCCH for the own device is present. Then, when the terminal detects presence of a PDCCH for the own device, the terminal starts receiving a PDSCH by detected downlink control information.
Further, in the LTE method, an operation performed when a terminal transmits a signal to a base station is as follows. When a terminal does not detect presence of a PDCCH for the own device, which is transmitted from a base station, the terminal transmits a PUCCH. On the other hand, when the terminal detects presence of a PDCCH for the own device, the terminal starts transmitting a PUSCH by detected uplink control information. Further, in this case, the base station performs a CRC (Cyclic Redundancy Check) check with respect to the received PUSCH, and transmits the check result to the terminal by a PHICH. The terminal performs uplink packet data re-transmission control on the basis of a CRC check result with respect to a PHICH from the base station.
In the LTE method, a DRX function is employed for the purpose of electric power saving of a terminal. The DRX function is a function of causing a terminal to sleep in a specific state and to stop monitoring a PDCCH for reducing electric power consumption of the terminal. Specifically, it is assumed that a terminal does not receive a PDCCH in an OnDuration section when the terminal is Active, because there is no data to be transmitted or received. In this case, a terminal having a DRX function decodes a PDCCH transmitted from a base station for scheduling only in a next OnDuration section. A section in which a terminal does not decode a PDCCH is referred to as a “DRX section.” On the other hand, when a terminal receives a PDCCH in an Active section, the terminal is allowed to activate a DRX Inactivity Timer (extend an Active section), and to continue data communication.
It is assumed that a terminal fails to receive a PDCCH due to a wireless error or the like, despite that a base station has transmitted the PDCCH to the terminal. In this case, when an Active section is extended only in the base station, wireless resources may be useless even when the base station continues scheduling and transmits a PDCCH, because the terminal is in a DRX section.
Various prior arts are proposed relating to the present invention.
For instance, PTL 1 describes packet re-transmission control by an HARQ. In a communication system disclosed in PTL 1, packet missing accompanied by a DTX to ACK error is detected without affecting an existing communication device. In this example, a DTX to ACK error is that a transmission-side communication device erroneously recognizes a DTX, specifically, absence of a re-transmission request from a receiving-side communication device as an ACK. A DTX to ACK error mainly occurs due to a decoding failure of a control channel in a receiving-side communication device.
The communication system disclosed in PTL 1 is constituted by a transmission-side communication device which transmits packets respectively added with sequence numbers and different from one another, and a receiving-side communication device which receives the packets. The receiving-side communication device includes a receiving unit and a determination unit. The receiving unit receives packets with use of a plurality of processes. The determination unit detects missing of reception of any one of the packets in the receiving unit on the basis of the sequence numbers. In this case, the determination unit determines whether or not the one packet is missing accompanied by a DTX to ACK error in the transmission-side communication device, on the basis of a use status of each process.
Further, PTL 2 discloses a technique capable of limiting a probability of a DTX to ACK error to an allowable level. A base station disclosed in PTL 2 includes an interface and a processor. The interface is configured to receive information included in acknowledgement/negative acknowledgement (ACK/NACK) resources in an uplink control channel, and relating to a generated bundled ACK/NACK value and relating to the number of downlink grants detected in a receiving bandwidth of a user device. The processor is configured to execute ACK/NACK/DTX (discontinuous transmission) detection on the basis of the received information, and to determine whether or not the detected ACK/NACK state reflects a proper ACK/NACK on the basis of the ACK/NACK/DTX detection.
PTL 3 discloses a re-transmission control method and a receiving-side device capable of minimizing packet missing when a transmission-side device erroneously detects delivery acknowledgement information transmitted via an HARQ feedback physical channel. The transmission-side device disclosed in PTL 3 includes an MAC multiplexing unit, an MAC header adding unit, and a shared physical control channel receiving unit. The receiving-side device includes a shared physical control channel transmitting unit.
The MAC header adding unit generates a protocol data unit (packet) to be transmitted on a transport channel, which is multiplexed in a shared physical data channel by adding an MAC header and an error-correcting code (such as a CRC) to user data transmitted from the MAC multiplexing unit. The shared physical control channel receiving unit receives delivery acknowledgement information such as an ACK/NACK via a shared physical control channel (HARQ feedback physical channel), and notifies an associated HARQ process of the information. The shared physical control channel receiving unit judges that the device is in a DTX state when the device does not receive delivery acknowledgement information with respect to each packet within a predetermined period of time. The shared physical control channel transmitting unit transmits delivery acknowledgement information (ACK/NACK) notified from each HARQ process via the shared physical control channel (HARQ feedback physical channel).
PTL 4 discloses a base station device and a communication control method capable of appropriately performing a scheduling process and an HARQ process in an LTE downlink and in an LTE uplink. The base station device disclosed in PTL 4 includes a baseband signal processing unit. The baseband signal processing unit includes a layer 1 processing unit.
The layer 1 processing unit performs demodulation and decoding of a CQI or delivery acknowledgement information to be mapped in an uplink control channel transmitted by an uplink. The layer 1 processing unit performs, in the subframe, a process of receiving delivery acknowledgement information or a CQI mapped in a physical uplink control channel (PUCCH) located on both sides of a system band, when delivery acknowledgement information or a CQI relating to a mobile station which does not receive user data is received in an uplink. Then, the layer 1 processing unit notifies an MAC processing unit of the delivery acknowledgement information or a receiving result of a CQI.
The delivery acknowledgement information described above is one of an ACK, a NACK, and a DTX. The DTX means that “a mobile station actually did not deliver delivery acknowledgement information.” When the delivery acknowledgement information is determined to be a ‘DTX’, the base station device re-transmits a downlink shared channel. Note that the scheduling process designates a process of sorting out mobile stations which receive user data with use of a shared channel in a downlink of the subframe.
PTL 5 discloses a terminal device and a re-transmission control method capable of improving characteristics of a response signal (an ACK/NACK signal, or “A/N”) having poor transmission characteristics. A base station disclosed in PTL 5 includes a data transmission control unit, a modulation unit, a PUCCH extraction unit, and a re-transmission control signal generation unit.
When the data transmission control unit receives a NACK or a DTX with respect to downlink data transmitted from the re-transmission control signal generation unit with use of a certain downlink unit band, the data transmission control unit outputs holding data associated with the downlink unit band to the modulation unit. When the data transmission control unit receives an ACK with respect to a downlink transmitted from the re-transmission control signal generation unit with use of a certain downlink unit band, the data transmission control unit deletes holding data associated with the downlink unit band.
The PUCCH extraction unit extracts, from a PUCCH signal included in a receiving signal, a signal in a PUCCH region associated with a bundled ACK/NACK resource, which is notified to a terminal in advance. Further, the PUCCH extraction unit extracts, from a PUCCH signal included in a receiving signal, an A/N resource associated with a CCE (Control Channel Element) occupied by a DPCCH used in transmitting downlink allocation control information (DCI), and a plurality of PUCCH regions associated with a plurality of A/N resources notified to a terminal in advance.